Conventional skateboards are equipped with steering mechanisms known as trucks. The trucks are mounted on the underside of a skateboard opposite to each other, one in the front and one in the rear. Each truck carries two wheels, one at each end of the truck's axle. Most skateboards are sold as separate elements, namely the deck, trucks, and wheels. These elements are assembled, together with a few accessories, by either the buyer or the retail seller.
The sport of skateboarding includes many different styles of competition, such as streetstyle, ramp riding, bowl riding, freestyle, slalom racing, and downhill racing. The equipment used in serious skateboarding pursuits must meet exacting performance requirements. The truck or chassis of the board determines many of the most crucial performance characteristics.
Skateboard trucks serve four main purposes: 1) to connect the skateboard's wheels to the skateboard deck; 2) to provide a wide-ranging steering response, whereby the wheel axles swivel to create a finite turning radius when, by means of lateral weight shifts, the skateboarder tilts the deck about its longitudinal axis; 3) by means of a suspension system, to smoothly and predictably resist the skateboarder's efforts to tilt the deck, thus stabilizing the vehicle during straight-ahead riding and providing control over the steering response; and 4) by means of the same suspension system, to generate a force which will quickly return the skateboard to the neutral, non-turning position after the skateboarder discontinues a lateral weight shift.
Skateboard dimensions have varied a great deal during the course of the sport's history. They also vary somewhat according to the preferences and habits of the user. At present, however, the decks on which skateboarders stand are usually about 9 to 10 inches wide and 30 to 31 inches long. Decks may be formed of laminated wood or other shaped material which provides a relatively flat center portion, viewing the board from nose to tail, often a slightly and gradually upturned nose, and usually a more sharply upturned tail portion. Throughout most of their length skateboard decks are wide enough to accommodate a skateboarder's foot positions angularly across the longitudinal axis of the board. Across their width skateboard decks usually have a concave profile to give the rider better feel for the edges of the skateboard.
Presently, skateboard wheelbases, that is, the distance from the front axle to the rear axle, average approximately 17 inches to 19 inches. The axles are usually about 9 inches long, and they carry wheels which are normally about 1.6 inches to 2.75 inches in diameter and 1 to 1.50 inches wide. The wheels are typically radiused on both the inside and outside edges, and they are usually made of urethane compositions.
Generally, a skateboarder stands on a skateboard deck with his feet approximately shoulder-width apart, the rear foot being placed on or near the upturned tail of the board and the forward foot being placed slightly behind the board's nose. For simple maneuvers, a skateboarder stands on the skateboard deck in a generally upright position. However, from instant to instant he may shift his weight from one side of the board to the other or toward the nose or the tail. For more intricate maneuvers, the skateboarder may shift his feet further apart, bracing them against the nose and tail curvatures of the deck, or closer together. He may crouch over the board, balancing himself with outstretched arms, forwardly-leaning shoulders and rearwardly-positioned buttocks. The wheels beneath the skateboard deck are located to accommodate both simple and intricate maneuvers, taking into account how far apart a skateboarder may position his feet and shift his weight for both types of maneuvers.
Ideally, a skateboarder should steer the skateboard in such a way that his body is leaning at the same angle as the skateboard deck is tilted. In other words, the skateboarder's body should remain perpendicular to the skateboard deck at all times. This allows the skater to center his movements in the pelvis, which in turn produces an optimal accord amongst muscular efficiency, balance, control, power, quickness, and traction. Yet, if the skateboarder is using ideal turning technique, the modern skateboard will turn stably at only one velocity. Depending on the brand of truck and the length of the wheelbase, this velocity will usually be between 3 and 6 miles per hour. Even at that speed, however, the steering response of the conventional truck is only roughly stable. At all other speeds, skateboarders are presently forced to compromise their skating form to compensate for the insensitivity of their trucks. It has, therefore, been extremely difficult for skateboarders to take full advantage of the turning action of their skateboards.
By altering the angle of the arm on which the wheel axles pivot, i.e., the angle between that arm and the longitudinal axis of the deck, or by varying the length of the skateboard's wheel base, it is possible to slightly increase or decrease the forward velocity at which the skateboard steers well. However, skateboards need to turn stably through a wide range of speeds.
Conventional skateboard trucks follow a basic design in which an axle pivots about an arm attached at one end to the center portion of the axle. The other end of this pivot arm is loosely fitted, at an angle of approximately 45.degree., into a plastic cup mounted in a baseplate, thus forming a ball-like joint. A pair of doughnut-shaped grommets, usually made of rubber or urethane plastic of varying hardnesses, is mounted on a substantially vertical king pin fixed in the baseplate on the side of the axle opposite the plastic cup. These grommets grasp a ring extending from the axle body so that the axle is suspended between the ball joint and the grommets. By adjusting the king pin, the tension on the grommets may be increased or decreased, thereby varying the balance between turning stability and turning ease. One example of this standard design is shown in U.S. Pat. No. 3,862,763, issued Jan. 28, 1975, to Gordon K. Ware.
The king pin employed in conventional skateboard trucks is oriented at a substantially right angle to the tilting movement of the deck, resulting in high stress on the king pin. Because the king pin and the grommets do not adequately stabilize the pivot arm axis, and because of the loose fit between the pivot arm and the plastic cup, the angle of the pivot axis tends to deteriorate as the axle tilts, so that very tight turns may be difficult or impossible to achieve.
A further drawback of this standard design is that the suspension system formed by the plastic grommets fails to provide fine steering control. Skateboarders control the angle of the deck's tilt, and thus the size of the turns they make, by varying the distance by which they shift their weight laterally across the width of the deck. Regardless of their hardness or of how they are adjusted, the standard urethane grommets do not offer a regular, orderly pattern of resistance to such weight shifts. The result is that skateboarders cannot easily predict or measure how far they must shift their weight to achieve steering radii of various sizes.
Also, conventional skateboard trucks generally mandate a severe trade-off between stability and maneuverability, such that skateboarders may achieve turning stability or turning ease, but usually not a combination of or balance between the two. Turning stability is understood to mean a relative insensitivity to sideward weight shifts, such that a skateboarder may fluctuate his body mass across much of the width of the deck without causing the skateboard to tilt or turn very much. Turning ease, or maneuverability, is understood to mean a relatively greater sensitivity to sideward weight shifts, such that a skateboarder may achieve tight turns through relatively smaller lateral displacements of his body mass. When adjusted to be relatively maneuverable, standard trucks tend to respond much too quickly to sideward weight shifts, thereby becoming disproportionately unstable, especially at high speeds. When adjusted to be relatively more stable, conventional trucks tend to respond much too slowly, thus losing most or all of their ability to make tight turns. A middle ground or compromise between turning ease and turning stability is thus difficult to achieve.
Moreover, when a skateboarder removes his weight from the side of the deck at the end of a turn, the plastic grommets used in conventional trucks do not return the skateboard to the neutral, non-turning position quickly enough. Sideward shifts of a skateboarder's body mass create forces which compress the grommets, thus causing the deck to tilt and the skateboard to steer. Conventional trucks behave like dampers in the sense that the energy used to compress the grommets is largely dissipated; the grommets retain very little of this energy for use in quickly rebounding the axles to the straight-ahead position. This is especially noticeable, and troublesome, when the skateboarder attempts to propel and accelerate himself by means of quick alternating turns. High-performance skateboarding depends upon the ability of the trucks to quickly resume straight-forward motion after the skateboarder discontinues a lateral weight shift.
Additionally, conventional skateboard trucks often begin to feel kinked, as if they "want" to steer in one direction more than the other, such as to the left more than to the right. The plastic cup in which the axle pivot arm swivels, and the urethane grommets, tend to permanently deform in an asymmetrical manner in accordance with the skateboarder's steering habits and may oppose his attempts to steer the skateboard either straight ahead or against the memory of the plastic cup and grommets.
Finally, conventional trucks feature irregular shapes on the sides which face the center of the skateboard, so that they may catch or hang up on the edges of objects which skateboarders may jump onto, such as curbs, low walls, or the lips of ramps and bowls. This may put the skateboarder at risk of harmful falls.
Heretofore in the patent art various forms of wheel suspension systems have been utilized in foot-operated rolling equipment such as roller skates. One such system is shown in U.S. Pat. No. 319,839 issued Jun. 9, 1885 to I. P. Nelson. In that patent, the shoe supporting deck portion of a roller skate is mounted on two trucks. Each truck includes a pair of helical springs, each with a lower end disposed against a plate on an axle carrying a set of wheels. The plate contains apertures for the lower ends of a pair of rods to slide through. The rods also extend through the centers of the springs and an adjusting nut on each rod is tightened down against the upper end of the spring to give it tension. Each rod hangs from a pair of lugs fastened to the underside of the shoe supporting deck. The springs and rods have their longitudinal axes in parallel planes which are normal to the shoe supporting deck. A rocker pin rotatably attaches the plate and axle to a hanging member depending from the underside of the deck between the springs so that the plate and wheel axle of each truck can move in a curved path beneath the shoe supporting deck. The office of the springs is to normally hold the skate deck parallel to the horizontal plane of the wheel-axles, under which conditions the two axles of the skate should be in parallel vertical planes. The lower ends of the rods slide up or down through the plate on the axle as one wheel or the other rises and returns to normal.
Another form of mechanism for permitting the wheels of a roller skate to move through an arcuate path against the tension of helical springs is shown in U.S. Pat. No. 321,434 issued Jul. 7, 1985 to O. Harrison. In that patent, a finger member called a T-piece is affixed to an axle housing, and the central leg of the T is disposed between the ends of two springs mounted opposite to each other on a common horizontal axis. As the axle in the had of the T moves through an arcuate path, the central leg of the T is resisted by one spring or the other.
Still another form of mechanism for controlling the arcuate movement of wheel axles beneath the deck of a roller skate is shown in U.S. Pat. No. 865,441 issued Sep. 10, 1907 to G. S. Slorum. The forward and rear trucks are fastened to the roller skate deck entirely with springs. In this assembly coil springs between the trucks are positioned with their longitudinal axes normal to the skate deck in all vertical planes. The springs will accommodate slight movements of the trucks in any direction and will act to cushion and take up any shocks or vibrations produced by running over uneven surfaces or by encountering slight obstacles.
Yet another form of spring suspension in the front truck of a roller skate is shown in U.S. Pat. No. 2,128,865 issued Aug. 30, 1938 to C. Vogt. Coil springs are disposed upon upright pins from a wheel truck. The pins extend partway up into the centers of the spring coils. The assembly is designed to dissemble slight shocks on the front wheels of the roller skate. The coil springs act between the upper surface of the skate deck and the under surface of the truck. The pivotal suspension permits the wheel truck to pivot slightly relative to the bracket to absorb shocks imparted to the front wheel assembly.
In U.S. Pat. No. 2,424,819, issued Jul. 29, 1947 to S. Guttridge, an axle housing having an axle, with wheels at its distal ends, is suspended well below the deck of a skate. The housing supports a pivot pin which is inclined at an upward angle toward the deck in a vertical plane. A yoke within the axle housing is resiliently clamped upon the pivot pin. Tapped holes in the axle housing communicate with the yoke and contain helically-shaped springs bearing at one end upon the yoke to press it into interlocking engagement with the pivot pin and bearing at the other end back upon screws plugging the springs, exits from their holes. The freedom of the pivot pin to turn against the yoke is thus regulated by the pressure bearing upon the pivot pin brought about by advancing and tightening the screws on the springs to force the yoke into contact with the pivot pin.
U.S. Pat. No. 2,537,213 shows a truck mounted on the underside of a skate deck. An arm with a ball at its upper end depends from a ball socket affixed immediately below the deck. The arm is arranged to twist in the socket and also to allow its lower end to move vertically against a pair of coil springs. An axle extends horizontally through a housing which is also attached at one end to the arm. The other end of the housing is engaged upon a floating pivot pin. Thus, the wheels on the axle can move vertically in concert or independently against the pair of coil springs biased against the arm, as well as pivoting from the ball and socket joint, and they may also pivot about the pivot pin which, in turn, floats against a third spring.
The skateboard truck shown in U.S. Pat. No. 4,054,297 provides a horizontal spindle parallel to the longitudinal axis of the skateboard for the axle of the truck to rock upon. A pair of plates affixed to the underside of the skateboard crosswise of the longitudinal axis hang the horizontal spindle between them beneath the skateboard. Above the horizontal spindle a plate is suspended beneath the longitudinal axis of the skateboard, and a pair of coil springs, each with an end pressing upon the plate, extend to the wheel axle carriage pivotally mounted upon the horizontal spindle. The springs are intended to keep the axle horizontally level beneath the board.